Interaction Between Nitrogen and Chemical Plant Protection in Yield Formation of Cereal Crops

Plant productivity is a result of an effect of yield promoting and yield protecting factors. The first group of the factors determines process of yield formation, including dry matter accumulation (plant growth) and differentiation of generative organs (plant development). The other group of the factors stabilizes previously created yield and protects it against reduction. Both groups of factors are influenced by weather conditions.


Introduction
Plant productivity is a result of an effect of yield promoting and yield protecting factors.The first group of the factors determines process of yield formation, including dry matter accumulation (plant growth) and differentiation of generative organs (plant development).The other group of the factors stabilizes previously created yield and protects it against reduction.Both groups of factors are influenced by weather conditions.
Among yield promoting factors nitrogen fertilization is the most important one.Nitrogen significantly increases grain yield by the influence on yield components formation at the course of plant development.The relationships are well described in the literature (Fotyma & Fotyma, 1993;Mazurek, 1999;Spiertz & Vos, 1983;Wyszyński et al., 2007).At early plant development stages nitrogen stimulates tillering process and therefore determines potential spike number per unit area and decides about final number of spikelets per spike.At stem elongation stage nitrogen protects a plant against excessive reduction of tillers and spikelets, which means that nitrogen enables big number of grains per spike.In the period before anthesis, nitrogen stimulates the effectiveness of assimilation of organs and production of biomass, which subsequently, at the grain filling stage participates in the photosynthesis process (Bertholdssson, 1999;Przulj & Momcilovic, 2001).During maturity, nitrogen affects grain quality.Restriction of N supply at any development stage can reduce grain yield by up to 65% (Zhao et al., 2009).
Despite nitrogen fertilization is the most important grain yield creating factor, the maximization of grain yield is possible only under conditions of a proper plant protection against fungal diseases.Plant protection is usually aimed at increasing the resistance to these diseases and to combat the already active pathogens.For these aims, specific programs are recommended to producers.However, the precedent purpose of the protection against fungal diseases is to preserve the yield against reduction and its stabilization (Pruszyński, 2002).In unprotected canopies fungal diseases reduce wheat potential yield by 45% on average and the losses may reach even 70% (Perrenoud, 1990;Podolska et al., 2004).Chemical protection measures extend plant green area and the duration of photosynthetic activity (Dimmok & Gooding, 2002;Ruiter & Brooking, 1996) and stimulate effects of grain yield promoting factors.The efficiency of the protection is related to the pattern of weather conditions, which simultaneously influences plant infestation by pathogens (Nowak et al., 2005).Higher precipitation, besides nitrogen fertilization and crop yields, usually favors also development of the fungal pathogens (McMullen, 2003).Deficit of precipitation restricts their development, and therefore the effect of chemical plant protection measures on grain yield is smaller (Brzozowska et al., 1996).
For best possible nitrogen utilization, all diseases should be avoided (Goulding, 2000).However, nitrogen fertilization increases the susceptibility of plants to fungal infections, and therefore the interaction between weather, nitrogen and plant protection strategy can be expected.The purpose of the study was to quantify this interaction in the production of four cereal crops: winter wheat, spring barley, winter triticale and oat under conditions of differentiated nitrogen fertilization rate.

Field site and management
The study was performed on the basis of a long term experiment in Grabów Experimental Station (E 21 o 39', N 51 o 21') of the Institute of Soil Science and Plant Cultivation in Puławy, Poland in 2004-2007.The experiment was located on a highly heterogenous soil that was classified partly as stagnic luvisol and partly as pseudo podzolic.Average soil reaction was slightly acid.
Four cereal crops winter wheat, spring barley, winter triticale and oat were grown in fourcourse crop rotation.The first experimental factor was the strategy of chemical plant protection against fungal diseases proposed by three companies: A, B and C and the control treatment without any protection.
Plant protection strategies differ in the selection of biologically active ingredients of the fungicides (tab.1).However, the strategies differentiate neither the level of plant infestation by pathogens nor the grain yield of cereals.Therefore, the results for strategies were treated as the additional replications and further on the average date for all of them are presented and discussed, against the control treatment.
Winter cereals were sown in mid-September and the spring cereals at the beginning of April (tab.2).Harvest time was from the end of July to the beginning of August.After harvest, at full maturity stage (BBCH 91) grain yield per plot was determined.

Disease incidence
In the vegetation periods 2005, 2006 and 2007 plant infection by fungal diseases was estimated at the plant milky maturity stage .Infection of three upper leaves

Statistical analysis
All data were statistically processed using analysis of variance by Statgraphics Centurion v. XV statistical package.The significance of differences between treatments (e.g.protection strategy, N rates and their interaction) were estimated by Tukey's test at α=0.05 confidence level.Regression analysis has been applied for calculating optimal nitrogen rate depending on protection treatments.

Weather conditions
Weather data originated from the Grabów meteorological station located close to the experimental field (tab.3).The data concerning precipitation and the mean daily temperature were used for calculations of Sielianow's index (K).The index is the product of the total precipitation (P) and sum of mean daily temperatures (t) in a given period:

Disease infestation
Weather conditions in study years differentiated development of fungal diseases, plant infection and efficiency of fungicides (tab. 4, 5, 6, 7).Among plant organs, leaves of studied crops appeared to be the most sensitive.Leaves of winter wheat in all years were infected by Stagonospora nodorum, Dreschlera tritici-repentis and Blumeria graminis (tab.4 The leaves of oat in each year were infected by Helminthosporium avenae and Puccinia coronata (tab.5).However the area of damaged leaves in 2005 and 2006 was small and equaled to 0.13 and 1.14%, respectively.In 2007 the infested area in not protected treatments was higher and equaled to 2.5%.The efficiency of fungicides in protection of oat against fungal diseases was generally low.Insignificant number of stems with necrotic pots proved its small sensitivity to fungal diseases and a good value as a preceding crop for the other cereals.Fungicides with the exception of triticale and barley in dry 2006, and oat in all years significantly decreased the infections of stem base by fungal diseases.However, their efficiency was much lower than against the infestation of leaves.
For winter triticale and spring barley, the protection measures were the most effective in 2005 (42% and 49%) and the least in 2006 (25% and 27%, respectively).Fungicides applied for winter wheat reduced infection by 31%, 36% and 21% in the consecutive study years.The effect in oat was not statistically proved in all study years.
The infection of the cereal crop root system was very low indeed.Infestation indexes were in the range of a few percent and did not influence crop productivity.
Generally, 2007 was the year of the highest fungal disease infestations of all parts of winter wheat and spring barley and generative parts of winter triticale and oat.The other parts of winter triticale, especially stem base and root system, were infected the most in 2005 and in 2006.Otherwise, in the 2006 year the infections of both winter crops leaves and winter wheat spikes and spring barley root system were very small.In 2005 year, the infections of both spring crops leaves and winter triticale spikes, winter wheat and spring barley stem base and winter wheat root system were limited.Chemical plant protection measures significantly reduced the fungal infections of all cereal crops except oat.As an average of four years grain yield of all cereals increased significantly to the highest applied rates of nitrogen (tab.8).However, the yield increases reached about 3,6 tone of grain for winter cereals and only about 2 tones for the spring ones.All the tested plant protection strategies proved to be effective in comparison to the control treatment.As it has been already mentioned, the differences between these strategies were rather insignificant and further on the average values for all strategies were discussed.Plant protection measures showed the highest efficiency for winter wheat and then for winter triticale and spring barley.Their efficiency for oat was practically negligible.
The most interesting are interactions between three factors influencing cereals yield.All interactions of the second order proved to be significant and are further presented on figures 1-4.
The effect of nitrogen was the highest in 2004 and the lowest in 2006 (fig.1).In 2004 characterized by moderate temperature and higher then long-term averages, rainfall.The highest nitrogen rates increased the yield of winter cereals by almost 6 ton and spring cereals by almost 3 ton of grain.In 2006, which was the driest one, the yield increases reached about 2 tons, only and for oat less than 1 ton of grain.In 2005 and 2007, the effects of nitrogen were rather similar, though the yield level was much higher in the former year.Both these years were characterized by moderate rainfall, but 2007 was significantly warmer.For winter wheat, the optimal nitrogen rates can be estimated at 160 kg N•ha-1 in 2004, 120 kg N•ha -1 in 2005 and 2007, and at about 80 N•ha -1 in 2006.For winter triticale and spring barley, the corresponding nitrogen rates were 120, 90 and about 60 kg N•ha -1 .For oat, in three study years, except 2004 with 120 kg N•ha -1 , the estimated optimal nitrogen rate was 60 kg N•ha -1 only.Chemical plant protection was the most effective in a wet and warm 2007 year and the least (for winter cereals) or not effective at all (for spring cereals) in the dry, though the rather cold 2006 year (fig. 2 ).In 2004 and 2005, the effect of plant protection measure was significant, however smaller than in 2007, for all cereals except oat.The yield increases of winter wheat and spring barley in the most prone to fungal diseases 2007 year were in the range of about 1 ton of grain per ha, while those for triticale and oat reached about 0.3 ton per ha only.

Fig. 2. Grain yield of cereal crops depending on plant protection strategy in 2004-2007
Nitrogen fertilization generally increased efficiency of plant protection measures for all cereals except oat (fig.3).This interaction was, however, strongly depended on the weather conditions in the study years.Only oat practically each year did not respond to plant protection measures.The year 2007 was the most effective for plant protection.The effect in grain yield raised according to nitrogen rate increase from 0.5 to 1.4 t•ha -1 for winter wheat, from 0.5 to 1.3 t•ha -1 for spring barley and from 0.04 to 0.7 t•ha -1 for winter triticale.Effect of oat plant protection ranged from 0.2 to 0.3 t•ha -1 .In 2004 chemical plant protection affected practically only winter wheat and winter triticale grain yield.
Dry weather in 2006 caused that crop protection was practically ineffective for spring crops, and the increase of winter wheat was reduced to 0.2-0.4t•ha -1 .Grain yield of winter triticale increased from 0.2 t•ha -1 in the control treatment to 0.6 t•ha -1 on the 90 kg N•ha -1 rate.Figure 3 allows for drawing the conclusion that without nitrogen fertilization and if the nitrogen rates are low, the application of fungicide is of no use and surely would bring economic losses.Another conclusion is that oat in Polish condition does not respond to plant protection measures.Interaction of plant protection against fungal diseases and nitrogen fertilization can be further analyzed from the side of nitrogen efficiency (fig.4).In all study years, except 2006 and for all cereals, except oat, nitrogen efficiency was higher in the treatments with fungicide application.The yield increases of winter cereals under an influence of high nitrogen rates were in the range 3 -6 tons of grain per ha in protected treatments and 2.3 -4.4 ton in the control.The positive interaction of nitrogen and plant protection measures was not so strong in the case of spring barley.The yield increases under nitrogen rates in protected treatments were by 0.3-0.5 ton grain per ha higher than in the control one.Besides in 2007 year, fungicide application for spring barley did not increase the efficiency of nitrogen at all.As results from figure 4, each next nitrogen rate more often gave a significant yield increase in protected treatments than in the control treatment.This problem will be more comprehensively presented in the discussion.

Discussion
Water availability in the growing season in Poland affects significantly plant growth and yield (Grzebisz, 2004).In the own study efficiency of plant protection measures and nitrogen efficiency were also modified by weather conditions.Hence, the interactions between weather, nitrogen and plant protection measures, including the yield level are quite complicated.

Weather conditions, diseases infestation and crop protection
It is practically known that climatic conditions and each weather anomaly (e.g.drought) might restrict development of pathogens (Garret, et al., 2006;Jaczewska-Kalicka, 2008;Korbas, 2008).Unfortunately, due to technical reasons crop infestation by fungal diseases was not estimated in 2004 year.The best conditions for disease infestation of leaves, stem base, and generative plant parts of winter wheat and spring barley crops were noted in 2007.However, this year was not so favorable for development of stem base diseases on triticale.
The year 2007 was characterized by high temperatures and precipitation in the whole vegetation season, except for April.Even in this year, the infestation of oat plant by all fungal diseases were negligible.The poorest conditions for leaf and generative plant parts infection of winter crops were noted in dry 2006.However, that does not concern the stem base diseases, which develop the best in this particular weather conditions.It reveals another problem in investigation on fungal diseases, namely different susceptibility of plant parts depending on the weather course (Bła ej &Bła ej, 2000;Garrett, et al., 2006;Jaczewska, 1993& Jaczewska-Kalicka, 2008).Anyway, among the studied crops, except barley in 2007, leaves were much less infected then culm base (tab.9).The level of infection depends considerably on the cereal crop.The cereals grown in the experiment can be ranked as follow in descending order concerning the sensitivity to fungal infection: winter wheat>winter triticale>spring barley>oat.
Chemical plant protection measures significantly reduced the infections of all cereals, except oat, with fungal diseases (tab.9).The efficiency of fungicides against leaf disease were higher than against the culm diseases.It should be noted that all studied protection strategies considered rather protection against diseases of leaves and spikes than stem base and root system.

Weather conditions and grain yield
The highest average yields of all cereal crops was recorded in a relatively cool and wet 2004.For winter cereals it was a combining effect of direct influence of favorable weather conditions on plant growth and development, very high nitrogen efficiency and positive effect of plant protection measures.The last of mentioned factor seems to be insignificant for spring cereals, particularly oat.These results are confirmed by Nowak et al., 2005, who has Interaction Between Nitrogen and Chemical Plant Protection in Yield Formation of Cereal Crops 181 found a similar combining effect of weather conditions and the level of plant infestation by pathogens on the cereals grain yield.Unfortunately, the data concerning plant infestation in this year are unavailable.The next good, and for oat very good, was 2005 year.In this year, high yield of grain were recorded already in control treatment and the efficiency of nitrogen fertilization was high.In 2005, the March and April were very dry but later on moisture conditions favored plant growth and development.As a matter of fact the level of plant infestation by pathogens was pretty high but so was the efficiency of fungicides.
In 2007 in spite of favorable weather conditions the yields of all cereals were lower than in 2005.For winter wheat and spring barley it can be explained by the highest infection of plants by pathogens in experimental period.The infection of winter triticale plants was in fact on average level but the efficiency of fungicides against culm diseases was rather low.
For the whole experimental period the lowest yields of all cereals were achieved in the cold and dry 2006 year.It is a combining effect of limitation in plant growth and development, as well as low nitrogen efficiency and high level of culm base infestation by pathogens.Low yields of cereal crops in dry years are well documented in the literature (Ferrante et al., 2008;Hura et al., 2007;Jessop, 1996;Okuyama, 1990;Pecio, 2002;Rodriguez-Pérez et al., 2007& Savin, 1996).
Special attention should be dedicated to oat.This crop gave low yields both in cold and dry 2006 year as well as in the moist and hot 2007 year.Oat, other cereal crops unlikely, requires lower temperatures and high air moisture for proper growth and development (Givens et al., 2004;Welch, 1995).According to Doehlert et al., 2001 the highest oat yield is obtained under conditions of warm, sunny weather in the spring and cooler summer, without excessive precipitation at grain filling stage.The results of Michalski et al., 1999 showed the decrease of oat productivity in line with increasing the temperature in the period between April and July with May as the month of the highest oat sensitivity.Our results confirmed that relationships.Higher temperatures in 2006 and 2007 years in the critical period of oat development decreased grain yield considerably.Furthermore, the highest mean temperature in May 2007 decreased grain yield comparing to 2006, independently of higher precipitation.
Our results suggest that weather conditions can modify yield of cereal grain more than infestations by fungal diseases.Grain yield of cereal crops and its variability between years is a result of many factors co-operating each with other throughout the whole vegetation period (Jaczewska-Kalicka, 2008).Garret et al., 2006, Gooding & Lafever, 1991, Mazurek, 1999& Welch, 1995 claim that weather conditions effect the plant development, nutrient uptake ability and photosynthesis effectiveness.They cause the changes in plant assimilation area and photosynthesis rate, which decides upon the quantity of storage materials in the seeds, and therefore, about its weight and grain yield per area unit.Adequate moisture conditions before anthesis enable plants to accumulate storage materials, which might be used for grain filling.After anthesis, plants stay green for longer time, which extends the period of grain filling stage and increases final grain yield (Coles et al., 1991).
Weather conditions in the study years explain only partly the differences between cereal grain yields.Our results confirmed the opinion of the other authors (Doehlert et al. 2001;Peterson et al. 2005), that grain yield is determined mainly genetically, and in turn it is strongly modified by weather conditions.Saastamonien et al. (1989) showed, that different cultivars of cereal crops can adopt to climatic changes in different ways.In the own research, the choice of varieties changed in experimental years.In 2004-2006, winter wheat variety Rywalka was grown, and in 2007 variety Turnia, both yielding on the similar level.The cultivars of spring barley were Justina and Rywalka.In the studies of Noworolnik (2003), Justina was distinguished by a high yield.Winter triticale was represented by Woltario (2004Woltario ( -2006) ) and Zorro varieties, both yielding on similar level.Among cultivars of oat, lower yielding Cwał variety was grown in the years 2005-2006, and high yielding Szakal cultivar in 2004 and 2007.

Nitrogen fertilization
Good supply of nitrogen decides upon proper plant growth and development (Fotyma, 1988;Spiertz & Vos, 1983).Availability of nitrogen for crop depends on the mineral nitrogen reserves in soil, supplemented by fertilizers and on soil moisture conditions.Supply of nitrogen also considerably influences plant susceptibility to pathogens, particularly fungal diseases (Krauss, 2001;Poschenrieder et al., 2006).In the own research, due to the application of five nitrogen rates, it was possible to interpret quantitatively the effect of nitrogen, using regression equations.The relations between cereal grain yield and nitrogen rates were the best approximated by a polynomial of second order (fig.6).The model was previously used by Fotyma, 1997;Fotyma, 1988;Fotyma, 2000& by Fotyma & Filipiak, 2008.
Applied regression model characterized by a "flat" part around the breaking point, usually overestimates the real effect of nitrogen on grain yield (Cerrato & Blackmer, 1990).For this reason, optimum N rate was calculated for 90% of maximal grain yield, according to the method described by Barłóg et al., 2008.Optimal nitrogen rates, securing this yield level, calculated from the regression equations are presented in table 10.In few cases, these rates were extrapolated and are included for general orientation only.From this table, several conclusions can be drawn.Optimal nitrogen rates were always higher for winter than for spring cereals.For spring barley and oat, nitrogen rates can be limited to about 100 kg N •ha -1 , while for winter cereals it should be increased by about 50%.
Optimal N rate depends strongly on the weather and in the vegetation season 2004, characterized by average Sielianinow's index K=1.9, for winter cereals this rate exceeds the top rate applied in the experiment.Optimal nitrogen rates for crops protected against fungal diseases, were also high in the years 2005 and 2007 with ample rainfall and Sielianinow's index in spring exceeding K=1.5.In the very dry 2006, the optimal nitrogen rates could be limited to about 100 kg N•ha -1 , even for winter cereals.Another very important conclusion is that optimal N rates for winter cereals, and in favorable weather conditions for spring cereals as well, were higher in the treatments with fungicide application.This regularity did not concern a very dry year of 2006, characterized by a very low efficiency of plant protection measures.The regularity is with agreement with other authors (Grzebisz, 2008;Jaczewska, 1993& Noworolnik, 2003).Another useful index for comparing nitrogen effect on cereal yield depending on weather conditions, nitrogen rate and plant protection measures is NUE (nitrogen use efficiency) (Potarzycki, 2010).This index gives the information on the yield increase per one kilogram of applied nitrogen (Nf) (Moll et al., 1982), and can be further used for economic calculations (fig.7).The analysis of NUE confirms already discussed relation between the nitrogen efficiency and weather as well as fungicide's application.Positive interaction between nitrogen rates and fungicides application is confirmed by many authors (Bradley et al., 2002& Delin et al., 2008).For the good nitrogen utilization, pest and diseases should be kept under control (Goulding, 2000).Gooding et al. 2005& Ruske et al., 2003 have reported that grain yield, crop biomass, grain nitrogen and thereby nitrogen use efficiency increase with decreasing incidence of fungal diseases and/or with crop protection.

Interaction and concurrence between nitrogen and plant protection measures
Interaction is a purely statistic term, used in processing the results of investigations by analysis of variance.In the further consideration more proper seems to be the term of concurrence, which does not have a strict statistical sense.The result concurrence between two factors can be synergistic, antagonistic and/or additive.The type of relation between nitrogen fertilization and plant protection measures will be analyzed here on the basis of the data presented in table 11.This table does contain neither the data for all cereals in 2006 year, nor the data for oat in all study years.It has previously been shown that this year was extremely dry and was characterized by a low efficiency of nitrogen fertilizer and practically no effect of plant protection measures.As one can conclude from this table, the main factor deciding upon yield increasing is nitrogen fertilization, while the effect of plant protection measures is much lower.However, similarly to Smagacz & Kuś, 2010, the effect of nitrogen, with few exceptions, was higher for protected cereals and the effect of plant protection was higher for cereals well supplied with nitrogen.On the average, the concurrence between the nitrogen and plant protection measures was of additive character.The combined effect of nitrogen fertilization and plant protection was the highest in 2004 year characterized by rather cold and wet weather.

Year
Nmax Winter cereals were more responsive to nitrogen fertilization and plant protection in comparison to spring barley, not to mention the unresponsive for protection oat.The own results are in some contradiction to those of Fotyma, 1999 andGrzebisz, 2008, who have found synergistic type of concurrence between the amount of applied N and wheat protection.The additive effect of nitrogen and fungicide follows the Law of Optimum (Claupen, 1993).Therefore, it should not be surprising than even in a very dry 2006, some effects of fungicide application were recorded, but they were reduced due to drought, which in turn decreased uptake of nitrogen.Nitrogen stimulates grain developing process and plant protection extends the period of a photosynthesis (Dimmok & Gooding, 2002;Ruiter & Brooking, 1996).Pruszyński, 2002, accented stabilizing but not promoting yield character of plant protection.It means that under conditions of poor plant infestation by pathogens, plant protection measures are unnecessary.However, abandoning the fungicide application under conditions of heavy infestation by pathogens can lead to complete yield lost.

Conclusion
Four study years represented satisfactorily the changeability of weather conditions in Poland.In the three of these four years, the routine programs of cereal's protection against fungal diseases, recommended by leading chemical companies, proved to be effective for winter wheat, winter triticale and spring barley.Oat practically does not respond positively to plant protection measures independently of weather.In the very dry year, all cereal crops except winter triticale do not need to be protected against fungal diseases.Nitrogen is the main factor deciding upon the yield increases of winter and spring cereals.Optimal nitrogen rates are always higher for winter than for spring cereals and depend considerably on the weather.There is a positive interaction between nitrogen and plant protection measures.Fungicide application is practically useless in cereals not well supplied with nitrogen from mineral fertilizers.The concurrence between nitrogen and fungicide application is of additive character.

Acknowledgment
The author would like to express gratitude to Syngenta, DuPont and BASF representatives for providing fungicides for the research.

Fungal
diseases infected also the stem base of plants, particularly the winter cereals.In the control treatment, as an average of 2005-2007 years the stem base of winter wheat showed the 51%, and winter triticale 44% level of infestation (tab.7).In these years infection index of spring barley equaled to 24% and of oat to about 2% only.The level of infestation depended on the weather in study years.Generally, winter wheat and spring barley were the most infected in 2007, much less in 2006, and the least in 2005.Different pattern of stem base infestation was recorded in triticale, which was the least infected in 2007 and more seriously in the years 2006 and 2005.Stem base of oat was practically healthy.

Fig. 3 .
Fig. 3. Effect of nitrogen rate on efficiency of chemical plant protection in 2004-2007

Fig. 6 .
Fig. 6.Regression curves for the relationships between grain yield and nitrogen fertilization rate

Fig. 7 .
Fig. 7. Agronomic Nitrogen Efficiency (kg of grain per kg Nf) in relation to nitrogen rate and crop protection .com Interaction Between Nitrogen and Chemical Plant Protection in Yield Formation of Cereal Crops 185

Table 5 .
Percent of damaged spring cereal crops leaf area by fungal pathogens in[2005][2006][2007]The generative parts of winter cereals were slightly infected, 2-6% of spikes area in 2005 and 2006 years and moderately infected, 8-9% of spikes area in 2007 (tab.6).Efficiency of fungicides against spikes infestation was pretty high and reached 60-80%.Generative parts of spring crops were not infected at all in 2005 and 2006, and only slightly infected in 2007 (about 5% of barley spikes and 2% of oat panicles).

Table 6 .
Total percentage of damaged cereal spike and panicle area by fugal pathogens in 2005-2007

Table 9 .
Leaf and culm infection of cereals in the years 2005-2007

Table 10 .
Optimal nitrogen rate securing 90% of maximal grain yield www.intechopen.comInteraction Between Nitrogen and Chemical Plant Protection in Yield Formation of Cereal Crops 183 Control Protection